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Gzip and Brotli Compression

In short

Gzip and Brotli are HTTP content encodings that reduce transferred text bytes when the server and browser negotiate a supported encoding.

Decision rule and boundaries

Gzip and Brotli are HTTP content encodings that reduce transferred text bytes when the server and browser negotiate a supported encoding. Content encoding is negotiated between client and server: a browser advertises acceptable encodings and the server returns a representation with Content-Encoding. It is most useful for compressible HTML, CSS, JavaScript, JSON, and SVG—not for already-compressed images or archives.

The diagram locates the rendering or measurement stage that this performance concept describes.

How to inspect it

Request a representative document with and without accepted encodings, then compare headers, transfer size, cache variation, and successful decoding. Confirm that an intermediary does not serve a Brotli representation to a client that did not negotiate it.

Practical workflow

Enable compression at the layer that owns delivery, keep Vary: Accept-Encoding where shared caching requires it, and verify a cold and cached response. Measure transfer bytes separately from server response time and rendering work.

Common mistakes and measurement limits

A smaller transfer does not prove a faster interaction. Compression cannot repair slow origin processing, oversized images, excessive JavaScript, or a cache configuration that delivers the wrong variant. The common failure mode is compressing already-compressed media or judging compression from an uncompressed local file.

FAQ

Gzip and Brotli are HTTP content encodings that reduce transferred text bytes when the server and browser negotiate a supported encoding.
Inspect Content-Encoding, Vary: Accept-Encoding, response size, and whether the decoded page still renders correctly, then record the source, date, configuration, and missing evidence.
Do not confuse one observation with a guarantee. A common error is compressing already-compressed media or judging compression from an uncompressed local file.